One type of fire control mechanism commonly used in semiautomatic handguns includes a hammer which is pivotable from a rearward cocked position to a forward position for impacting the firing pin. A sear releasably retains the hammer in its cocked position with the hammer spring or main spring in compression. When the trigger is actuated, the sear is moved to release the hammer that is moved by the stored energy of the main spring, to strike the firing pin which is thereby driven forward to fire a chambered round. The principal drawback of this type of mechanism is that it includes numerous parts and is relatively complex and expensive to manufacture.
Another common configuration is disclosed in U.S. Pat. No. 3,857,325 to Thomas wherein a striker type firing pin is utilized in lieu of a pivotable hammer. Upon actuation of the trigger, a trigger bar operated sear engages a projection that extends from the firing pin and moves the firing pin rearward, thereby to compress a firing pin spring. When the trigger is moved a predetermined distance rearward, the sear will be moved to release the firing pin projection whereby the firing pin spring will drive the firing pin in a forward direction with sufficient force to fire a chambered round.
This mechanism has at least one principal disadvantage in that there is no provision for disconnecting the sear from the trigger to allow the sear to move independently back into the path of the firing pin during the recoil of the slide. The absence of this feature makes for a gun having a relatively low rate of fire. In addition, this mechanism may be difficult to manufacture and its components subject to fatigue and failure with extensive usage.
Other configurations which utilize firing pin striker mechanisms include those disclosed in U.S. Pat. Nos. 4,539,889; 4,825,744 and 4,893,546 issued to Glock. In all but one of the configurations of the above referenced patents, which discloses a hammer for engaging the firing pin, an abutment is provided to alternately engage and disengage the nose of a firing pin. When the trigger is actuated, the abutment engages the downwardly depending nose of the firing pin and moves the same rearwardly until the nose and the abutment have reached a predetermined position. With the firing pin at that position, the spring will have been compressed and various control or camming means are disclosed for moving the abutment out of the path of the firing pin nose whereby the firing pin spring will impel the firing pin with sufficient force to fire a chambered round.
One of the principal characteristics of such prior art handguns is that, due to the recoil forces and machining tolerances of the handguns, the firing mechanism may not perform in the manner intended. In certain cases the handgun may have either repeated firings stemming from a single activation of the trigger, while in other cases, the handgun may not fire at all upon subsequent activation of the trigger.
Such handguns can therefore be said to have a measured amount of firing uncertainty, this uncertainty increasing as the wear on the constituent elements of the handgun increases.